Double wall structure

ABSTRACT

A double wall structure capable of suppressing an increase in a sound transmission amount with regard to sound with a specified frequency and stably exhibiting a sound insulation performance for sound with various frequencies is provided. 
     A double wall structure  1  is assumed to be a door serving as a part of an automobile. The double wall structure  1  is provided with plate-like bodies  2  and  3  arranged in parallel and opposing to each other with leaving a predetermined distance. The plate-like bodies  2  and  3  are formed in a rectangular shape with one direction being slightly longer. Between the two plate-like bodies  2  and  3  opposing to each other is formed an internal chamber  4 . Side plates  5  are provided so as to connect the plate-like bodies  2  and  3  to each other, and thereby the internal chamber  4  is almost closed. At a position where a sound pressure is increased in the internal chamber  4  is provided a sound absorbing chamber structure  6  having a porous surface  6   a  on one surface in a rectangular parallelepiped.

TECHNICAL FIELD

The present invention relates to a double wall structure for insulating sound from a noise generating source for a part of a bag structure in a vehicle body of an automobile such as a door, a hood and a trunk lid.

BACKGROUND ART

Conventionally, there is a proposed technique that a double wall structure is used for the door, the hood, the trunk lid or the like serving as a part used in the automobile (for example, refer to Patent Documents 1 and 2). A configuration of the above conventional example is schematically shown in FIG. 26. A double wall structure 1′ of the above conventional example has a hollow box shape in which between plate-like bodies 2 and 3 opposing to each other with leaving a predetermined distance is formed an internal chamber 4, and the internal chamber 4 is closed by side plates 5.

However, in the double wall structure 1′ shown in Patent Document 1, (a) when a sound wave of a noise is incident from the upper side and the noise includes a sound component with a specified frequency, resonance in the internal chamber 4 (resonance mainly in the direction parallel to the plate-like bodies 2 and 3) is generated with regard to the sound component so that amplitude of the plate-like body 2 on the lower side serving as a radiation surface is increased, and hence an increase in a radiated sound reduces a sound insulation performance; or (b) although the double wall structure 1′ constitutes a vibration system with three elements of the plate-like body 2, the air in the internal chamber 4 (working as a spring) and the plate-like body 3, there is sometimes a case where the resonance is generated in the vibration system with regard to the noise with a specified frequency so that the sound insulation performance is reduced.

Patent Document 1: Japanese Patent Laid-Open No. 2002-96636 Patent Document 2: Japanese Patent Laid-Open No. 2003-118364 DISCLOSURE OF THE INVENTION

The present invention is achieved in consideration to the above point, and an object thereof is to provide a double wall structure capable of suppressing an increase in a sound transmission amount with regard to sound with a specified frequency, and stably exhibiting a sound insulation performance for sound with various frequencies.

The double wall structure according to the present invention has plate-like bodies opposing to each other, a completely or almost closed internal chamber being formed between the plate-like bodies, the double wall structure comprising a sound absorbing chamber forming shell forming a sound absorbing chamber provided in at least one plate-like body among the plate-like bodies, the sound absorbing chamber forming shell being adjacent to the plate-like body and isolated from the internal chamber, and a sound pressure reducing portion for reducing a sound pressure in the internal chamber, the sound pressure reducing portion having a number of through portions passing through the sound absorbing chamber forming shell or the plate-like bodies so as to open the sound absorbing chamber to the internal chamber.

In the double wall structure according to the present invention, the sound pressure reducing portion having a number of the through portions for opening the sound absorbing chamber to the internal chamber is formed in the sound absorbing chamber forming shell or the plate-like bodies. It should be noted that the “closing” does not only mean strict sealing but also includes a case where there is partially a clearance or an opening. The sound absorbing chamber serving as a sound absorbing mechanism is preferably formed in the vicinity of a part with a high sound pressure in a resonance state of the internal chamber.

In the case where sound excitation is applied from one side of the double wall structure, the resonance is generated within the internal chamber. By a sound absorbing effect of the sound pressure reducing portion, it is possible to effectively reduce the sound pressure of the internal chamber. Thereby, since a sound excitation force to the radiation surface of the other side of the double wall structure is reduced, it is possible to reduce vibration amplitude of the radiation surface and improve sound transmission loss. It should be noted that the sound absorbing effect of the sound pressure reducing portion is generated by energy dissipation due to friction in an inner wall surface of the through portion when the resonance is generated in a spring-mass system in which the air within the sound absorbing chamber is the spring and the air inside the through portion is a mass. Therefore, a size of the sound absorbing chamber, a specification of the through portion (a diameter and an aperture ratio) and the like have to be designed so that a frequency of the resonance of the internal chamber to be suppressed (that is, a frequency to improve sound transmission loss) substantially corresponds to a resonance frequency of the spring-mass system of the sound absorbing chamber and the through portion. In the case where the through portion is minute, the energy dissipation due to a vortex generated in the vicinity of the through portion is added and hence a larger sound absorbing effect is generated in a wider frequency range.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of an embodiment 1-1 of a double wall structure according to the present invention.

FIG. 2 is a schematic perspective view of an embodiment 1-2.

FIG. 3 is a schematic perspective view of an embodiment 1-3.

FIG. 4 is a schematic perspective view of an embodiment 2-1.

FIG. 5 is a schematic perspective view of an embodiment 2-2.

FIG. 6 is a schematic perspective view of an embodiment 2-3.

FIG. 7 is a schematic perspective view of an embodiment 2-4.

FIG. 8 is a schematic perspective view of an embodiment 2-5.

FIG. 9 is a schematic perspective view of an embodiment 2-6.

FIG. 10 is a schematic perspective view of an embodiment 2-7.

FIG. 11 is a schematic perspective view of an embodiment 3-1.

FIG. 12 is a schematic view showing an example of a cross section of a sound absorbing chamber structure.

FIG. 13 is a schematic view showing an example of the cross section of the sound absorbing chamber structure.

FIG. 14 is a schematic view showing an example of the cross section of the sound absorbing chamber structure.

FIG. 15 is a schematic view showing an example of the cross section of the sound absorbing chamber structure.

FIG. 16 is a schematic view showing an example of the cross section of the sound absorbing chamber structure.

FIG. 17 is a schematic view showing an example of the cross section of the sound absorbing chamber structure.

FIG. 18 is a schematic view showing an example of the cross section of the sound absorbing chamber structure.

FIG. 19 is a schematic view showing an example of the cross section of the sound absorbing chamber structure.

FIG. 20 is a schematic view showing an example of the cross section of the sound absorbing chamber structure.

FIG. 21 is a schematic view showing an example of the cross section of the sound absorbing chamber structure.

FIG. 22 is a schematic view showing an example of the cross section of the sound absorbing chamber structure.

FIG. 23 is a view showing an effect of the double wall structure according to the present invention.

FIG. 24 is a view showing an effect of the double wall structure according to the present invention.

FIG. 25 is a view showing an effect of the double wall structure according to the present invention.

FIG. 26 is a schematic perspective view of a conventional double wall structure.

BEST MODE FOR CARRYING OUT THE INVENTION

Next, a description will be given to embodiments of the present invention. It should be noted that in the present embodiments, a description will be given to a sound absorbing chamber structure as an example of a sound absorbing chamber forming shell. FIGS. 1 to 22 show embodiments of a double wall structure respectively, and FIGS. 23 to 25 show the effects of the double wall structure. Hereinafter, a description will be given in order.

FIG. 1 is a schematic perspective view showing an example of the double wall structure according to the present embodiment. A double wall structure 1 of an embodiment 1-1 schematically shown in FIG. 1 is assumed to be a door serving as a part of an automobile.

The double wall structure 1 is provided with plate-like bodies 2 and 3 arranged in parallel and opposing to each other with leaving a predetermined distance. The plate-like bodies 2 and 3 are formed in a rectangular shape with one direction being slightly longer. Between the two plate-like bodies 2 and 3 opposing to each other is formed an internal chamber 4. Side plates 5 are provided so as to connect the plate-like bodies 2 and 3 to each other, and thereby the internal chamber 4 is almost closed. In other words, the double wall structure 1 of the present embodiment is formed in a box shape in which the plate-like bodies 2 and 3 serving as double walls and the side walls 5 surround the internal chamber 4.

In the present embodiment, at a position where a sound pressure is high in the internal chamber 4 is provided a sound absorbing chamber structure 6 having a porous surface (sound pressure reducing portion) 6 a in which a number of holes (through portions) are formed on one surface in a rectangular parallelepiped. As a material of the sound absorbing chamber structure 6 having the porous surface 6 a, all of materials capable of forming the plate-like bodies such as iron, aluminum, resin and paper, or porous foil-like bodies and the like can be used.

It should be noted that in the present embodiment, the sound absorbing chamber structure 6 is formed in a rectangular parallelepiped and has an independent internal chamber (hereinafter, referred to as a sound absorbing chamber). Lower ends of three sound absorbing chamber structures 6 are arranged within the internal chamber 4 and in contact with a surface of the plate-like body 2 on the radiation side. Specifically, the sound absorbing chamber structure 6 and the plate-like body 2 are jointed by adhering with an adhesive or the like. It should be noted that the porous surface 6 a is not necessarily be parallel to the plate-like bodies 2 and 3. The present invention is not limited to providing three sound absorbing structures 6 but may be provided with one large sound absorbing chamber structure 6 and the inside thereof may be partitioned into three.

It should be noted that when determining an installment position of the porous surface 6 a, a position where the sound pressure is increased due to resonance in the internal chamber 4 is determined by numerical calculation with the finite element method or the boundary element method or by manufacturing and measuring an actual structure, and the porous surface 6 a is arranged at the above position. However, there are many cases where the position theoretically determined by calculation and the position where the sound pressure is actually the highest do not strictly correspond to each other and are different from each other. Therefore, the position where the sound absorbing chamber structure 6 is actually arranged is not strictly limited to the position where the sound pressure is increased but may be a position in the vicinity of the above position.

It should be noted that in the present embodiment, although the sound absorbing chamber structure 6 is provided on the plate-like body 2 side, the present invention is not limited to the above but the sound absorbing chamber structure 6 may be provided on the plate-like body 3 side.

When sound excitation is applied from the upper side to the plate-like body 3 side in the above configuration, the plate-like body 3 is vibrated so that the resonance is generated within the internal chamber 4. However, the sound pressure of the internal chamber 4 is reduced by a sound absorbing effect of the sound absorbing chamber structure 6. Therefore, since vibration amplitude of the plate-like body 2 on the lower side serving as a radiation surface is reduced, it is possible to decrease a radiated sound from the plate-like body 2 and improve sound transmission loss of the double wall structure.

FIG. 2 shows an embodiment 1-2. In the above configuration, four sound absorbing chamber structures 6 are arranged in the lengthwise and crosswise directions (each two sound absorbing chamber structures in the longitudinal direction and the lateral direction respectively). That is, since the number of the sound absorbing chamber structure 6 is increased from the case of the embodiment 1-1, areas of the sound absorbing chamber and the porous surface 6 a are increased and hence it is possible to improve sound transmission loss.

FIG. 3 shows an embodiment 1-3. In the above configuration, porous surfaces 6 a and 6 b are formed in the sound absorbing chamber structure 6. Therefore, since areas of the porous surfaces 6 a and 6 b of the four sound absorbing chamber structures 6 are increased, it is possible to further improve sound transmission loss. It should be noted that the number of the sound absorbing chamber structure 6 is not limited to three or four, but the optimum number may be determined in consideration to a resonance mode due to a noise assumed within the internal chamber 4. Further, hole diameters of the porous surfaces 6 a and 6 b may be optimally adjusted respectively.

FIG. 4 shows an embodiment 2-1. In the above configuration, an opening 2 b is provided in a part of a plate-like body 2 a on the radiation side (a perforated member). A plate-like body 7 serving as one of a closing member is provided so as to close the opening 2 b. The sound absorbing chamber structure 6 is jointed to a surface of the plate-like body 7. That is, the sound absorbing chamber structure 6 and the plate-like body 7 are jointed with the adhesive or the like. A description will be given later to other examples and the like of the above joint state.

When the sound excitation is applied from the upper side to the plate-like body 3 side in the above configuration, the plate-like body 3 is vibrated so that the resonance is generated within the internal chamber 4. The sound pressure of the sound absorbing chamber is reduced by the sound absorbing chamber structure 6. Therefore, since amplitude of the plate-like bodies 2 a and 7 on the lower side serving as the radiation surfaces is reduced, it is possible to decrease the radiated sound from the plate-like bodies 2 a and 7 and improve sound transmission loss of the double wall structure.

FIG. 5 shows an embodiment 2-2. The embodiment 2-2 corresponds to a combination of the embodiments 1-2 and 2-1. That is, the four sound absorbing chamber structures 6 are arranged in the lengthwise and crosswise directions (each two sound absorbing chamber structures in the longitudinal direction and the lateral direction respectively), and jointed to the surface of the plate-like body 7. In the above configuration, since the number of the sound absorbing chamber structure 6 is increased from the case of the embodiment 2-1, the areas of the sound absorbing chamber and the porous surface 6 a are increased and hence it is possible to improve sound transmission loss.

FIG. 6 shows an embodiment 2-3. The embodiment 2-3 corresponds to a combination of the embodiments 1-3 and 2-1. That is, the sound absorbing chamber structure 6 has the porous surfaces 6 a and 6 b, and the four sound absorbing chamber structures 6 are arranged in the lengthwise and crosswise directions (each two sound absorbing chamber structures in the longitudinal direction and the lateral direction respectively) and jointed in contact with the surface of the plate-like body 7. In the above configuration, since the areas of the porous surfaces 6 a and 6 b of the four sound absorbing chamber structures 6 are increased, it is possible to improve sound transmission loss. It should be noted that the number of the sound absorbing chamber structure 6 is not limited to three or four, but the optimum number may be determined in consideration to the resonance mode due to the noise assumed within the internal chamber 4.

FIG. 7 shows an embodiment 2-4. In the above configuration, embossment having a concavity and convexity shape is provided on the surface of the plate-like body 7 of the embodiment 2-3. Therefore, it is possible to enhance rigidity of the plate-like body 7. By using a plate-like body 7 a provided with the embossment in a concavity and convexity shape with enhanced rigidity, it is possible to improve workability of the plate-like body 7 a as well as a sound absorbing property. It should be noted that although the description is given to the embossment as a representative example of the concavity and convexity shape in the present example, the present invention is not limited to the above, and other arbitrary concavity and convexity shapes may be formed.

FIG. 8 shows an embodiment 2-5. In the above configuration, a vibration damping material 7 b is adhered to the surface of the plate-like body 7 of the embodiment 2-3. Therefore, the vibration is reduced by the vibration damping material of the plate-like body 7 b provided on the radiation surface side. As a result, it is possible to improve sound transmission loss.

FIG. 9 shows an embodiment 2-6. In the above configuration, a porous plate 7 c is used instead of the plate-like body 7 of the embodiment 2-3.

When the sound excitation is applied from the upper side to the plate-like body 3 side in the above configuration, the plate-like body 3 is vibrated so that the resonance is generated within the internal chamber 4. The sound pressure of the internal chamber 4 is reduced by the sound absorbing chamber structure 6 and the porous plate 7 c. Therefore, since amplitude of the plate-like bodies 2 a and 7 c on the lower side serving as the radiation surfaces is reduced, it is possible to decrease the radiated sound from the plate-like bodies 2 a and 7 c and improve sound transmission loss of the double wall structure.

FIG. 10 shows an embodiment 2-7. In the above configuration, a material of the plate-like body 7 of the embodiment 2-3 is formed of a porous body 7 d. For example, an example of the porous body 7 d includes a sound absorbing material formed of a fiber system such as grass wool and PET resin, or foam formed of open cells such as urethane. It should be noted that although the entire plate-like body 7 is formed of the porous body 7 d, the present invention is not limited to the above, and a part of a laminated thin film structure may serve as the porous body 7 d and be used in combination with the porous plate.

In the above configuration, the sound absorbing property is improved by the porous body 7 d of the plate-like body 7. At the time, the sound pressure of the internal chamber 4 is reduced by the sound absorbing chamber structure 6 and the porous body 7 d. Therefore, since amplitude of the plate-like bodies 2 a and 7 d on the lower side serving as the radiation surfaces is further reduced, it is possible to further decrease the radiated sound from the plate-like bodies 2 a and 7 d and improve sound transmission loss.

Next, FIG. 11 shows an embodiment 3-1. In the above configuration, a frame body 1 c formed of a plate-like body 2 c and side walls 5 c is attached from the lower side of the double wall structure 1 of the embodiment 2-1. By attaching the frame body 1 c, the plate-like body 7 is sandwiched by the plate-like bodies 2 a and 2 c. It should be noted that the frame body 1 c is attached so as to provide a clearance between the plate-like bodies 2 a and 7 and the plate-like body 2 c.

By the above configuration, in correspondence with the sound excitation applied from the plate-like body 3 side, the plate-like body 3 is vibrated so that the resonance is generated within the internal chamber 4. However, the sound pressure of the internal chamber 4 is reduced by the sound absorbing chamber structure 6 adhered and fixed to the plate-like member 7. Since amplitude of the plate-like body 2 c on the lower side serving as the radiation surface is reduced, it is possible to improve sound transmission loss of the double wall structure.

Next, a description will be given to the sound absorbing chamber structure 6. FIGS. 12 to 15 are explanatory views on an internal structure of the sound absorbing chamber structure 6.

FIG. 12 is a schematic sectional view showing the case where the sound absorbing chamber structure 6 is formed in a part of the plate-like body 2. In the above case, a lid member 61 is provided along a surface of the plate-like body 2. In the case where the configuration of FIG. 12 is applied to the embodiments 2-1 to 2-7 and 3-1, the sound absorbing chamber structure 6 is formed in a part of the plate-like body 7 instead of the plate-like body 2.

FIG. 13 is a schematic sectional view showing the case where the sound absorbing chamber structure 6 is formed in a part of a sound absorbing chamber structure supporting member 6 c.

In the above case, the sound absorbing chamber structure supporting member 6 c is provided in substantially parallel to the plate-like body 2 or 7. In the above case, a clearance may be provided between the sound absorbing chamber structure supporting member 6 c and the plate-like body 2 or 7, or conversely, no clearance is provided.

FIG. 14 is a schematic sectional view showing the case where the sound absorbing chamber structure 6 is formed in a container shape with one surface thereof opened, and the surface of the sound absorbing chamber structure 6 is substantially closed by the plate-like body 2 or 7.

In the above case, a part of the sound absorbing chamber structure 6 is screwed to the plate-like body 2 or 7. Therefore, it is possible to enhance the rigidity of the sound absorbing chamber structure 6.

Next, FIG. 15 is a schematic sectional view showing the case where the sound absorbing chamber structure 6 is formed in a rectangular parallelepiped container shape having the internal chamber 4.

In FIG. 15, the sound absorbing chamber structure 6 is jointed to the surface of the plate-like body 2 or 7 with an adhesive 80.

In any case of FIGS. 12 to 15, the sound absorbing chamber structure 6 is fixedly installed on the surface of the plate-like body 2 or 7. Therefore, when the sound excitation is applied from the upper side of the double wall structure 1 to the plate-like body 3 side, the plate-like body 3 is vibrated so that the resonance is generated within the internal chamber 4. At the time, the sound pressure of the internal chamber 4 is reduced by the sound absorbing chamber structure 6. Therefore, since amplitude of the plate-like body 2 on the lower side serving as the radiation surface is reduced, it is possible to decrease the radiated sound from the plate-like body 2 and improve sound transmission loss of the double wall structure.

Next, FIGS. 16 to 20 are schematic sectional views for showing a shape of the sound absorbing chamber structure 6.

FIG. 16 is a schematic sectional view showing the case where the sound absorbing chamber structure 6 is formed from a rectangular parallelepiped.

As shown in FIG. 16, as well as the embodiment 1-1, the porous surface 6 a is preferably formed in substantially parallel to the plate-like body 2. As in the embodiment 1-3, the porous surface 6 b may be formed with the porous surface 6 a substantially perpendicularly to the plate-like body 2 (not shown).

FIG. 17 is a schematic sectional view showing the case where the sound absorbing chamber structure 6 is formed in a shape in which a cylinder is vertically divided.

In the above case, the porous surface 6 a is formed on the almost entire surface of the divided cylinder shape sound absorbing chamber structure 6 x. It should be noted that in FIG. 17, although the description is given to the divided cylinder shape sound absorbing chamber structure 6 x, the present invention is not limited to the above, and may be a sound absorbing chamber structure formed of other arbitrary curved surfaces such as an ellipse. Although the porous surface 6 a is formed on the entire surface, the present invention is not limited to the above, and the porous surface 6 a may be formed on a part thereof.

Next, FIG. 18 is a schematic sectional view showing the case where the sound absorbing chamber structure 6 is formed in a conduit shape forming a polygon cross section (a pentagon in the figure) between the sound absorbing chamber structure 6 and the plate-like body 2 or 7.

In the above case, the porous surface 6 a is formed on the almost entire surface of the polygon conduit shape sound absorbing chamber structure 6 y. It should be noted that in FIG. 18, although the description is given to the polygon conduit shape sound absorbing chamber structure 6 y, the present invention is not limited to the above, and a sound absorbing chamber structure may be formed from a part of the polygon conduit shape sound absorbing chamber structure 6 y. Further, although the porous surface 6 a is formed on the entire surface, the present invention is not limited to the above, and the porous surface 6 a may be formed on a part thereof.

FIG. 19 is a schematic sectional view showing the case where the sound absorbing chamber structure 6 is formed in a conduit shape with a V-shape cross-section.

In the above case, the porous surface 6 a is formed on the almost entire surface of the V conduit shape sound absorbing chamber structure 6 z. It should be noted that in FIG. 19, although the description is given to the V conduit shape sound absorbing chamber structure 6 z, the present invention is not limited to the above, and a sound absorbing chamber structure may be formed from a part of the V conduit shape sound absorbing chamber structure 6 z. Although the porous surface 6 a is formed on the entire surface, the present invention is not limited to the above, and the porous surface 6 a may be formed on a part thereof.

FIG. 20 is a schematic sectional view showing the case where the sound absorbing chamber structure 6 is formed in a cylindrical shape.

In the above case, the porous surface 6 a is formed in a part of the cylindrical shape sound absorbing chamber structure 6R. The cylindrical shape sound absorbing chamber structure 6R is adhered and fixed to the plate-like body 2 or 7 with the adhesive 80.

It should be noted that in FIG. 20, although the description is given to the cylindrical shape sound absorbing chamber structure 6R, the present invention is not limited to the above, and a sound absorbing chamber structure may be formed from a part of the cylindrical shape sound absorbing chamber structure 6R. Although the porous surface 6 a is formed in a part thereof, the present invention is not limited to the above, and the porous surface 6 a may be formed on the entire surface.

In the above embodiment, although the description is given to the configuration that the sound absorbing chamber structure 6 is arranged between the plate-like bodies 2 and 3 (within the internal chamber 4), the sound absorbing chamber structure 6 can be arranged at a position outside the plate-like body 2 or 3 as shown in FIG. 21.

In an embodiment shown in FIG. 21, since the sound absorbing chamber structure 6 is attached on a lower surface of the plate-like body 2, the sound absorbing chamber is formed between the sound absorbing chamber structure 6 and the plate-like body 2. A porous surface (a sound pressure reducing portion) 2 d in which a number of holes (through portions) are formed is provided in the plate-like body 2 so as to communicate with the internal chamber 4 between the plate-like bodies 2 and 3 and the sound absorbing chamber.

When the sound excitation is applied from the upper side to the plate-like body 3 side in the above embodiment, the plate-like body 3 is vibrated so that the resonance is generated within the internal chamber 4. However, the sound pressure of the internal chamber 4 is reduced by the sound absorbing effect of the sound absorbing chamber structure 6. Therefore, since vibration amplitude of the plate-like body 2 on the lower side serving as the radiation surface is reduced, it is possible to decrease the radiated sound from the plate-like body 2 and improve sound transmission loss of the double wall structure.

In the above embodiment, since the sound absorbing chamber can be formed at positions outside both the plate-like bodies 2 and 3, it is possible to ensure a wide space (the internal chamber 4) on the inside of both the plate-like bodies 2 and 3 while exhibiting a sound pressure reducing effect mentioned above. Therefore, according to the above embodiment, even in the case where predetermined equipment is arranged within the internal chamber 4, it is possible to maintain a high degree of freedom of the arrangement so as to improve efficiency of an arrangement work of the equipment, while exhibiting a high sound insulation effect.

Further, as shown in FIG. 22, in the configuration provided with the plate-like body 2 a in which the opening 2 b is provided and the plate-like body 7 for closing the opening 2 b, it is possible to attach the sound absorbing chamber structure 6 on an outer surface of the plate-like body 7.

In the above embodiment, the sound absorbing chamber is formed between the sound absorbing chamber structure 6 and the plate-like body 7. A porous surface (a sound pressure reducing portion) 7 e in which a number of holes (through portions) are formed is provided in the plate-like body 7 so as to communicate with the internal chamber 4 and the sound absorbing chamber.

In order to confirm effectiveness of the above embodiments, the following experiments are conducted. That is, the double wall structures 1 of the structures of the embodiments 1-1 to 1-3 and 2-1 to 2-7 are installed at positions between both a sound source chamber and a sound receiving chamber in a reverberation chamber formed of the sound source chamber and the sound receiving chamber. On the basis of JIS A1416, a proper noise is generated from one side of the double wall structures 1, and the sound pressure is measured on the both sides sandwiching the double wall structures 1 with using a noise meter so as to determine sound transmission loss.

Results thereof are shown in FIGS. 23 to 25. It should be noted that results of similar experiments performed with regard to the structure of the conventional example (FIG. 26) are also shown in graphs of FIGS. 23 to 25. As shown in the graphs of the figures, sound transmission loss is dropped in a frequency area around 315 Hz in the conventional example. It is assumed that the resonance is generated in the above part.

Meanwhile, in the configuration of the embodiments of the present invention, as a result of reducing the sound pressure by the sound absorbing chamber structure 6 having the porous surface 6 a at a position where the sound pressure is increased, or as a result of reducing the resonance of a vibration system, it is found that a sound insulation performance can be improved.

Although the preferred embodiments of the present invention are shown above, a technical scope of the present invention is not limited to the above embodiments, but can be changed and performed in various ways.

For example, the double wall structure 1 according to the present invention can be applied not only to the door of the automobile, but also to a hood and a trunk lid for example. It is needless to say that the shape of the plate-like bodies 2 and 3 is not limited to the rectangle mentioned above, but can be variously changed in accordance with a shape of parts required.

Although the sound absorbing chamber structure 6 is jointed to the plate-like body 2 on the radiation side, the present invention is not limited to the above, and the sound absorbing chamber structure 6 may be jointed to the plate-like body 3 on the incident side.

The direction of the porous surface 6 a may be arbitrarily determined in consideration to various situations such as a positional relationship with a noise source.

Further, as the porous body 7 d, it is possible to use for example polyurethane, the foam formed of the open cells in addition to the grass wool mentioned above, a felt and the like. Through holes of the porous plate 7 c are preferably minute so that a viscous effect in the air passing through the holes can be expected.

In the above embodiments, although the description is given to an example that a number of holes (through portions) are formed as the porous surfaces 2 d, 6 a and 7 e, the through portions are not limited to the holes, but can be slits for example.

The present invention is described in the above preferred embodiments but is not limited to the above. It can be understood that various other embodiments are performed without departing from the spirit and the scope of the present invention. Further, in the present embodiments, although operations and effects by the configuration of the present invention are described, the operations and effects are only examples and do not limit the present invention.

That is, the present invention has the following configuration at least.

(1) The double wall structure according to the present invention has plate-like bodies opposing to each other, a completely or almost closed internal chamber being formed between the plate-like bodies, the double wall structure comprising a sound absorbing chamber forming shell forming a sound absorbing chamber provided in at least one plate-like body among the plate-like bodies, the sound absorbing chamber forming shell being adjacent to the plate-like body and isolated from the internal chamber, and a sound pressure reducing portion for reducing a sound pressure in the internal chamber, the sound pressure reducing portion having a number of through portions passing through the sound absorbing chamber forming shell or the plate-like bodies so as to open the sound absorbing chamber to the internal chamber.

In the double wall structure according to the present invention, the sound pressure reducing portion having a number of the through portions for opening the sound absorbing chamber to the internal chamber is formed in the sound absorbing chamber forming shell or the plate-like bodies. It should be noted that the “closing” does not only mean strict sealing but also includes a case where there is partially a clearance or an opening. The sound absorbing chamber serving as a sound absorbing mechanism is preferably formed in the vicinity of a part with a high sound pressure in a resonance state of the internal chamber.

In the case where sound excitation is applied from one side of the double wall structure, the resonance is generated within the internal chamber. By a sound absorbing effect of the sound pressure reducing portion, it is possible to effectively reduce the sound pressure of the internal chamber. Thereby, since a sound excitation force to the radiation surface of the other side of the double wall structure is reduced, it is possible to reduce vibration amplitude of the radiation surface and improve a sound transmission loss. It should be noted that the sound absorbing effect of the sound pressure reducing portion is generated by energy dissipation due to friction in an inner wall surface of the through portion when the resonance is generated in a spring-mass system in which the air within the sound absorbing chamber is the spring and the air inside the through portion is a mass. Therefore, a size of the sound absorbing chamber, a specification of the through portion (a diameter and an aperture ratio) and the like have to be designed so that a frequency of the resonance of the internal chamber to be suppressed (that is, a frequency to improve sound transmission loss) substantially corresponds to a resonance frequency of the spring-mass system of the sound absorbing chamber and the through portion. In the case where the through portion is minute, the energy dissipation due to a vortex generated in the vicinity of the through portion is added and hence a larger sound absorbing effect is generated in a wider frequency range.

(2) The sound absorbing chamber forming shell can be provided in an inner surface of the plate-like bodies, and the sound pressure reducing portion is provided in at least a part of the sound absorbing chamber forming shell.

In the above case, by providing the sound absorbing chamber forming shell in the inner surface of the plate-like bodies, it is possible to form the sound absorbing chamber at a position on the inside of both the plate-like bodies.

(3) The sound absorbing chamber forming shell can be provided in an outer surface of the plate-like bodies, and the sound pressure reducing portion can be provided in at least a part of the plate-like bodies.

In the above case, by providing the sound absorbing chamber forming shell in the outer surface of the plate-like bodies, it is possible to form the sound absorbing chamber at a position on the outside of both the plate-like bodies. Therefore, it is possible to ensure a wide space (the internal chamber) on the inside of both the plate-like bodies, while exhibiting the sound pressure reducing effect mentioned above. Consequently, according to the above configuration, even in the case where predetermined equipment is arranged within the internal chamber, it is possible to maintain a high degree of freedom of the arrangement so as to improve the efficiency of the arrangement work of the equipment, while exhibiting a high sound insulation effect.

(4) At least one plate-like body among the plate-like bodies can be provided with a perforated member in which an opening for opening the internal chamber to the outside is formed, and a closing member attached to the perforated member so as to close the opening, and the sound absorbing chamber forming shell can be provided in the closing member.

In the above configuration, the closing member provided with the sound absorbing chamber forming shell is installed for the opening formed in a part of the perforated member. It should be noted that the “closing” does not only mean strict sealing but also includes the case where there is partially the clearance or the opening. The sound absorbing chamber serving as the sound absorbing mechanism is preferably formed in the vicinity of the part with the high sound pressure in the resonance state of the internal chamber.

In the above case, since the internal chamber of the double wall structure is closed, when the sound excitation is applied from one side of the double wall structure, the resonance is generated within the internal chamber. However, by the sound absorbing effect of the sound pressure reducing portion, it is possible to effectively reduce the sound pressure of the internal chamber. Thereby, since the sound excitation force to the radiation surface of the other side of the double wall structure is reduced, it is possible to reduce the vibration amplitude of the radiation surfaces and improve sound transmission loss.

(5) The closing member may include a vibration damping member formed of a structure or a material having a vibration damping property. It should be noted that the vibration damping member includes a plate-like body in which a vibration damping material is laminated, and a plate-like body in which a constraint plate is laminated through the vibration damping material. It should be noted that the closing member includes a plate-like member or a sheet like body. The sheet like body means a body which is thinner than a plate such as a coat, a foil and a film, and a metal foil, a resin coat, cloth, a nonwoven fabric or the like can be used.

Even in the case where the sound excitation is applied by the above configuration, since the closing member itself has the vibration damping property, it is possible to reduce amplitude of the closing member itself and stably exhibit the sound insulation performance. It should be noted that as means for providing the vibration damping property of the closing member, the plate-like member may be the vibration damping member (such as a vibration damping steel plate, a vibration damping aluminum plate, and a vibration damping resin), or the vibration damping material (such as a vibration damping rubber, and the vibration damping resin) may be adhered to the plate-like member.

(6) The closing member may include a concavity and convexity member. It should be noted that an example of processing for providing the concavity and convexity member includes embossment.

In the above case, since the rigidity and the vibration damping property of the closing member can be enhanced, it is possible to reduce amplitude of the plate-like member itself and stably exhibit the sound insulation performance.

(7) The closing member preferably includes a structure or a material having a sound absorbing property. In the above case, the sound absorbing property can be improved by not only the sound pressure reducing portion but also the closing member and the resonance of the internal chamber can be reduced. Therefore, it is possible to stably exhibit the sound insulation performance.

(8) The closing member preferably comprises a porous body. It should be noted that the number of the porous body is not limited to one, but may be a plurality of porous bodies, or may be formed by laminating the porous body and a porous plate.

In the above case, the sound absorbing property can be improved by not only the sound pressure reducing portion but also the closing member and the resonance of the internal chamber can be reduced. Therefore, it is possible to stably exhibit the sound insulation performance.

It should be noted that as a design condition of holes, it is possible to use a design condition described in Japanese Patent Laid-Open No. 2003-050586 for example. Specifically, the design condition with regard to the porous plate of the above sound pressure reducing portion can be set so that for example a plate thickness, a hole diameter and an aperture ratio satisfy a design condition for generating the viscous effect in the air passing through the through portions.

As a result of facilitating conversion of air vibration due to the viscous effect into thermal energy by the double wall structure provided with the sound pressure reducing portion having a number of the through portions, a sufficient sound absorbing performance is surely exhibited in a wide frequency bandwidth. Thereby, an excellent sound absorbing performance is obtained for not only the noise of resonance frequency but also the noise of other frequency.

Further, in a part of the double wall structure having a number of the through portions, for example the frequency bandwidth with a sound absorption coefficient of 0.3 or more may be set to 10% or more with regard to the resonance frequency of the sound absorbing chamber. Further, the aperture ratio of a number of the through portions may be 3% or less. Further, the diameter of the through portions may be 3 mm or less, and a sound source of an object to which the sound insulation is performed may be 70 dB or more.

It should be noted that the diameter of the through portions is preferably 1 mm or less. It should be noted that since the diameter according to the present invention is provided in the sound pressure reducing portion, even the diameter of the through portions of 0.2 mm or less can be used.

(9) A plurality of the sound absorbing chamber forming shells may be provided in one of the plate-like bodies, and a plurality of sound absorbing chambers may be formed by the sound absorbing chamber forming shells.

In the above case, since a plurality of the sound absorbing chambers are formed by a plurality of the sound absorbing chamber forming shells, a specification (the diameter of the through portions, the thickness of the plate in which the through potions are formed, a thickness of an air layer, the aperture ratio and the like) can be changed for each of the sound absorbing chambers. Therefore, it is possible to suppress a number of resonances and improve sound transmission loss.

(10) The sound absorbing chamber forming shell may be provided with a partition member, and the sound absorbing chamber may be partitioned into a plurality of small chambers by the partition member.

In the above case, since a plurality of the small chambers are formed by the partition member, the specification (the diameter of the through portions, the thickness of the plate in which the through potions are formed, the thickness of the air layer, the aperture ratio and the like) can be changed for each of the small chambers. Therefore, it is possible to suppress a number of resonances and improve sound transmission loss. The number of the above plate in which the through portions are formed is not limited to one, but a plurality of plates may be laminated or may be formed in a multiple layer with leaving a space (a clearance).

(11) The sound absorbing chamber forming shell may include a concavity and convexity shape.

In the above case, since the sound absorbing chamber forming shell itself includes a concavity and convexity shape, it is possible to improve a processing performance in processing such as deep drawing, strength against the vibration and the like at the time of forming the sound absorbing chamber forming shell. The concavity and convexity shape may be included in a part of the sound absorbing chamber forming shell, and the concavity and convexity shape may be formed on the entire sound absorbing chamber forming shell. It should be noted that the processing for providing the concavity and convexity shape includes processing by the embossment or the like.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to suppress an increase in a sound transmission amount with regard to sound with a specified frequency, and stably exhibit the sound insulation performance for sound with various frequencies. 

1. A double wall structure having plate-like bodies opposing to each other, a completely or almost closed internal chamber being formed between said plate-like bodies, comprising: a sound absorbing chamber forming shell forming a sound absorbing chamber provided in at least one plate-like body among said plate-like bodies, the sound absorbing chamber forming shell being adjacent to said plate-like body and isolated from said internal chamber; and a sound pressure reducing portion for reducing a sound pressure in said internal chamber, the sound pressure reducing portion having a number of through portions passing through said sound absorbing chamber forming shell or said plate-like bodies so as to open said sound absorbing chamber to said internal chamber.
 2. The double wall structure according to claim 1, wherein said sound absorbing chamber forming shell is provided in an inner surface of said plate-like bodies, and said sound pressure reducing portion is provided in at least a part of said sound absorbing chamber forming shell.
 3. The double wall structure according to claim 1, wherein said sound absorbing chamber forming shell is provided in an outer surface of said plate-like bodies, and said sound pressure reducing portion is provided in at least a part of said plate-like bodies.
 4. The double wall structure according to claim 1, wherein at least one plate-like body among said plate-like bodies is provided with a perforated member in which an opening for opening said internal chamber to the outside is formed, and a closing member attached to said perforated member so as to close said opening, and said sound absorbing chamber forming shell is provided in said closing member.
 5. The double wall structure according to claim 4, wherein said closing member includes a vibration damping member formed of a structure or a material having a vibration damping property.
 6. The double wall structure according to claim 4, wherein said closing member includes a concavity and convexity shape.
 7. The double wall structure according to claim 4, wherein said closing member includes a structure or a material having a sound absorbing property.
 8. The double wall structure according to claim 4, wherein said closing member comprises a porous body.
 9. The double wall structure according to claim 1, wherein a plurality of said sound absorbing chamber forming shells are provided in one of said plate-like bodies, and a plurality of sound absorbing chambers are formed by said sound absorbing chamber forming shells.
 10. The double wall structure according to claim 1, wherein said sound absorbing chamber forming shell is provided with a partition member, and said sound absorbing chamber is partitioned into a plurality of small chambers by said partition member.
 11. The double wall structure according to claim 1, wherein said sound absorbing chamber forming shell includes a concavity and convexity shape. 